H870 would be a great powder, especially in the 257 and the 6.5mm versions but it tend to be a little pissy with temp variations and its getting very hard to find.

I will be using Retumbo for the lighter bullets and H-50 BMG for the heavies, I will even try some AA 8700 with the heavies to see what it does.

Rest assured, there will be some 100 gr Bonded Core FBHPs screaming down range. I'm going to run these girls through their paces so do not worry about the light bullet tests, they will be there as well.

Probably not down to the 85 gr pills but certainly the 100 gr bullets will be tested, just to see how they perform. If I can get velocities as consistant as the STW will with the 100 gr pills, I will offer data for that bullet as well but I suspect velocity spreads will be quite high with this light bullet in the larger case. With the improved shoulder angle, this may help efficency though compared to the STW.

Certainly not my friend. I use the Lilja 3 grooves in every high performance round I build if it is my choice.

Teh main benefit of the 3 groove design is longer throat life. This is a result of the lands being thicker then a conventional land. This thicker land resists errosion much longer because there is more steel to hold together.

Think of it like this.

Imagine a room with a temp of 80 degrees with two tables in them.

One table has six ice cubes on it that are 1" square spaced evenly apart in a circle.

The other table has only three ice cubes but they are 3" square each.

It will take much longer for the three larger cubes to melt compared to the six smaller cubes simply because the larger pieces of ice will resist melting longer then the small cubes.

Same way with the 3 groove vs 6 groove rifling. The 3 groove lands have alot more metal to erode so it takes longer to erode it.

Other advantages are decreased bore fouling and bore heat(again an aid to longer barrel life). This is a result of the bullet being engraved less by the fewer sharp edges of the rifling.

And yes, they are a bit faster.

Even with conventional twists and conventional bullets, the 3 groove barrels are my choice. They will be the only barrels I fit to my AM rounds simply because they will increase throat life a measurable amount over a standard rigling count.

In my opinion, they are just as if not more useful in conventional rounds as they are in the fast twist rifles.